The present invention relates generally to a press roller and, more particularly, to a press roller with adjustable bowing means.
Press rollers of the type which permit adjustable bowing under load are known in the prior art. See, for example, GB-PS No. 1,255,453. In particular, it is known to use press rollers of the type which include a bowing support or "cross head" which extends through a hollow, rotatable roller casing. In order to transmit the pressing force from the roller casing to the cross head, a pressure chamber into which pressurized fluid can be introduced, is utilized. The chamber faces towards the counter-roller with the aid of sealing strips.
When operating such press rollers, particularly wet presses in paper making machines, oftentimes the rollers would begin to oscillate due to reasons heretofore unexplained.
It has been found that such prior oscillation problems were caused by the combination of two oscillation systems both of which display at approximately the same frequency. One of the oscillating systems was the cross head which tends to undergo a bending oscillation, normally in the form of the second harmonic oscillation (i.e., there are four node points, two of which are in the cross head bearings and two of which are at the one-third points lying in between). The second oscillation system is a so-called contact oscillation of the press roller casing relative to its counter-roller. The occurence of this type of oscillation is obviously enhanced by the compressible felt strip running between the two rollers.
If the roller casing of the press roller is supported on the cross head at both ends via bearings and if, as in the above-mentioned known design, the distance between the roller casing bearings is less than the distance between the cross head bearings, there becomes a danger of a direct link-up between the said two oscillation systems.
Against the foregoing background, it is a primary object of the present invention to provide a roller which eliminates or at least minimizes these oscillations as much as possible.